Critical Heat Flux of R134a and R245fa Inside Small-Diameter Tubes

This article presents new experimental critical heat flux results under saturated flow boiling conditions for a macro/microscale tube. The data were obtained in a horizontal 2.20-mm inside diameter stainless-steel tube with heating lengths of 361 and 154 mm, R134a and R245fa as working fluids, mass velocities ranging from 100 to 1500 kg/m(2)-s, critical heat flux from 25 to 300 kW/m(2), exit saturation temperatures of 25, 31, and 35 degrees C, and critical vapor qualities ranging from 0.55 to 1. The experimental results show that critical heat flux (CHF) increases with increasing mass velocity and inlet subcooling but decreases with increasing saturation temperature and heated length. The data also indicated a higher CHF for R245fa when compared with R134a at similar conditions. The experimental data were compared against four CHF predictive methods and the results of the comparisons are reported.